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RFNC Photon Spectra from H2O, SiO2 and NaCl

 1. Name of Experiment: 
    Measurement of Photon Leakage Spectra from Spherical and Hemispherical Samples
    of H2O, SiO2 and NaCl compounds with a Central 14-MeV Neutron Source.

 2. Purpose and Phenomena Tested: 
    Measurement of spectra and leakages of photons from thick spherical and
    hemispherical samples of widespread earth’s crust elements irradiated with a
    Central 14-MeV Neutron Source for validation of existing nuclear data on gamma-
    production of these elements.

 3. Description of the Source and Experimental Configuration: 
    For these measurements has been using the same equipment as for paper [1].
    An installation NG-200 (200-KeV deuteron accelerator with the current of separated
    D+ ion beam of up to 1 mA) was used as 14-MeV neutron source. The target was placed
    in the center of spherical samples of inside diameter 100 mm and outside diameter
    200 mm. 

 4. Measurement System and Uncertainties: 
    The measurements were performed using a scintillation detector having a stilbene
    crystal with dimensions of  60x60 mm.
    Gamma-neutron separation was done using the scintillation pulse shape. 
    Direct 14-MeV neutrons from the target that were not scattered by the sample were
    delayed by a steel rod of diameter 30 mm and length 400 mm, placed in the immediate
    vicinity of the sample.
    Between the source and the detector, a concrete 1.5-m thick wall with a collimator
    was situated. To reduce the background of scattered photons and cosmic rays the
    detector was placed in a shield of 50-mm thick lead bricks. In addition, to reduce
    the background from secondary gamma-rays falling on the detector due to interaction
    of neutrons with materials surrounding the detector, a polyethylene cylinder of
    diameter 100 mm and length L=200 mm was placed into the collimator. The cylinder
    substantially (approximately by 10 times) absorbed neutrons and not very heavily
    (2-3 times) absorbed gamma-rays.

    The 14-MeV neutron flux was measured with an all-wave detector pre-calibrated in
    absolute measurements of the neutron flux of the installation. These absolute
    measurements were conducted using the activation method and the reaction
    Al-27(n,alpha)Na-24. When replacing the samples, the indications of the all-wave
    detector were adjusted according to the flux amplification/attenuation coefficient
    of the samples used. The coefficients were measured experimentally as a
    relationship of count rate of the all-wave detector with and without the sample.

 4.1. Measuring equipment and processing of experimental spectra.
    The photon spectrum measurements were conducted using a scintillation detector
    having a stilbene crystal with dimensions of 60x60 mm. Measured energy range is
    0.3 - 8.0 MeV. Energy resolution for lines Co-60 (1.17 and 1.33 MeV) was about 10%.
    At energies higher than 3 MeV it was 6-7% and at energies less than 0.5 MeV it was
    Processing of experimental electron-recoil spectra for transferring them into the
    photon spectra, was conducted using the method of “generalized differentiation”. 
    The results of measurements are presented in Table 2.

 4.2. Measurement uncertainty.
    The measurement uncertainty is a sum of the following components: 
    Statistical uncertainty Delta1=+-5 %. 

    Uncertainty in the detector efficiency.
    The detector efficiency was determined by measuring the spectra of standard
    preparations of Na-22, Cs-137, Co-60, Na-24. Within the energy range 0.5 - 3.0 MeV
    this uncertainty is estimated as ±5 %. Within the range 3 - 8 MeV the efficiency
    uncertainty may reach Delta2=7-8% due to the absence of standard preparations
    reference specimens with such energy. Uncertainty in mathematical processing of
    the experimental spectra is Delta3=+-7%. Sum of the above mentioned uncertainties
    is 12%.

    Possible uncertainty of the both sphere radii is ±1 mm and possible uncertainty
    of target unit dimensions is ±0.1 mm.

 5. Description of Results and Analysis; Comparison with Calculations: 
    The MCNP input used in the analysis is provided in mcnp5.inp. The d-t source is 
    described as monochrome (14 MeV) and isotropic. According to the author of the
    experiment these simplifications could effect the neutron measurements, but are
    insignificant for photon measurements. Using the MCNP input and the explanation
    in the text more detailed source description can be prepared. Figure 2 provides
    some details of the target unit allowing an explicit modeling of the (d-t) reaction,
    if some users may wish to do it. Arrangement of the layers at the end of target tube
    in the direction of the d beam is as follows:
    - Zr foil saturated with t (0.05 mm thick), placed in the center of the spheres
    - Cu (3 mm thick)
    - water used as coolant (1.5 mm)
    - Cu (0.5 mm)
    The uncertainty of the above values is about 0.1 mm.

    The gap between Fe and Cu (mats. 2 and 3 in Fig. 2) on the side surface is also
    filled with water.

    Figures 5-9 show that the photon spectra are very various and individual for each
    compound. The spectra of the hemispheres repeat the structure of the sphere’s. This
    shows the high relative accuracy of the measurements performed. In some cases the
    spectra calculated using the code MCNP and library ENDF/B-VI rel.6 differ greatly
    from the experiments and fall far outside the limits of experimental uncertainty.

    * H2O. All the experimental gamma-peaks are visible in the calculation spectra too.
    They agree on the height. The 2.25 MeV peak is produced on hydrogen (H) and other
    peaks are on oxygen (O). The main peaks 3.72, 613 and 7.1 MeV and some small peaks
    are identified in the measurements and the calculations. The annihilation peak
    0.51 MeV is present in all the experiments and calculations.

    * SiO2. In the range < 1.5 MeV, as for water one needs taking into account the
    neutron generator target construction and the container. Elsewhere the calculated
    gamma leakage is underestimated by two times and the 0.85 MeV peak is absent.
    The main peaks are 1.78 MeV on Si and 3.72, 613 and 7.1 MeV on O. Two close peaks
    2.75 MeV on O and 2.82 MeV on Si are joined in one. All the experimental gamma-peaks
    are visible in the calculated spectra but many of them are underestimated. It
    requires an essential increasing of the gamma-production on the Si nuclei.    

    * NaCl. All the main experimental gamma-peaks (0.44, 1.28, 1.65, 2.20 and 3.50 MeV)
    are visible in the calculated spectra too but a lot of them are underestimated.
    It requires an essential increasing of the gamma-production on the Na and Cl nuclei.

    There are significant discrepancies in gamma-production of the calculations and the
    experiments for these elements. The accepted nuclear data should be appropriately

    Any extrapolation of the leakage photon data in uninvestigated neutron energy
    intervals will be unreliable. Experiments on gamma-production for neutron energy
    range 5 - 10 MeV are necessary.
 6. Special Features: 
    Method of generalized differentiation with semi-empirically determined coefficients
    in order to transfer apparatus electron-recoil spectra into energy spectra.

 7. Author/Organizer 
    Experiment and Analysis:
    A.I. Saukov, V.D. Lyutov, E.N. Lipilina
    Institution: RFNC-VNIITF

    Compiler of data for SINBAD:
    A.I. Saukov, V.D. Lyutov, E.N. Lipilina
    Institution: RFNC-VNIITF

    Reviewer of compiled data:
    I. Kodeli
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France

 8. Availability: 

 9. References: 
    [1] A.I. Saukov, V.D. Lyutov, E.N. Lipilina, "Photon Leakage Spectra from Al, Ti,
        Fe, Cu, Zr, Pb, U-238 Spheres", SINBAD Database, OECD NEA Data Bank, France,
        Paris, identifier NEA-1517/72, 2006.

 10. Data and Format: 


        Filename    Size[bytes] Content 
    --------------- ----------- ------------- 
  1  rfnc_g2-a.htm      11.139 This information file
  2  rfnc_g2-e.htm      12.450 Description of experiment
  3  mcnp5.inp           2.624 Input data for the MCNP5 calculation
  4  Fig1geo.jpg        74.898 Fig. 1. Geometry of experiment
  5  Fig2mishen.jpg     85.485 Fig. 2. Design of the target unit
  6  Fig3na22.jpg       45.163 Fig. 3. Gamma-spectrum of Na-22 specimen
  7  Fig4na24.jpg       40.857 Fig. 4. Gamma-spectrum of Na-24 specimen
  8  Fig5h2osph.jpg    224.529 Fig. 5. Photon spectra from H2O sphere (calculated and experimental)
  9  Fig6sio2sph.jpg   228.391 Fig. 6. Photon spectra from SiO2 sphere     (-"-)
 10  Fig7sio2hsph.jpg  237.976 Fig. 7. Photon spectra from SiO2 hemisphere (-"-)
 11  Fig8naclsph.jpg   232.400 Fig. 8. Photon spectra from NaCl sphere     (-"-)
 12  Fig9naclhsph.jpg  212.783 Fig. 9. Photon spectra from NaCl hemisphere (-"-)
 13  tab1samples.txt       158 Table 1. Parameters of samples used
 14  tab2res.txt         4.545 Table 2. Results of measurements
 15  tab2res.xls        25.600 Table 2. Results of measurements (XLS format)

SINBAD Benchmark Generation Date: 5/2007
SINBAD Benchmark Last Update: 5/2007